This invention relates to a magnetically floating carrier system suitable for use in transporting articles which are brittle, fragile and susceptible to dust, such as semiconductors, and a carriage thereof.
In a conventional magnetically floating carrier system, a carriage body is driven by a linear motor while the body is kept afloat by floating magnets attracted to the bottom of the rails. The load is suspended with a pair of arms provided at the bottom of the carriage body and adapted to be closed by a spring force or the like.
In this type of carrier system, when the attraction caused by the floating magnets ceases, guide rollers mounted on the carriage body are adapted to be supported on guide rails laid on the ground to prevent the carriage body from falling.
The structure of the prior art system is disclosed in detail e.g. in Japanese Patent Unexamined Publication 1-126113.
In the above-described conventional system, if the arms are not hooked securely, or if shock is applied to the carriage body, e.g. at an emergency stop, the arms might be unhooked, allowing the load to drop.
Also, at a branching point of the track, the guide rails had to be cut off partially to allow the passage of floating magnets or a secondary conductor plate (reaction plate) of a linear motor which is mounted on the carriage body. This might cause the carriage itself to drop. Thus, the prior art system has much room for improvement in connection with safe transportation.
Also, there are the following problems.
1) It is necessary to provide movable arms on the carriage and a mechanism for opening and closing the arms on the ground. Thus, the mechanism for transferring loads tends to be complicated.
2) Because the position and size of the arms are fixed, the size and shape of the article that can be loaded are limited.
3) Movable parts provided on the arms and the carriage, such as a magnet suspension device, or contact portions between guide rollers and rails, are sources of dust. Since the load is located under these dust sources, it is difficult to provide a perfect protection against dust.